Think long and hard about your daily life and obligations, and your personal best and most productive times of the day. Decide how many days a week you are willing to devote to your writing. Add an extra day to that.
Now mark on your calendar the days and time you will devote to your writing. If you have to, wake up an hour early or stay up an hour later than you are used to.
By scheduling in your writing time, you'll be more apt to stick to the schedule. Plus, when friends or family or work request/demand your time, you'll more easily be able to tell them the truth:
I have a pre-arranged appointment at that time. We'll have to come up with another time.
Without the pre-scheduled time, chances are much greater that you'll put yourself and your writing last, which invariably means you'll not get to it.